In optical communications networks, optical communications modules are used to transmit and/or receive optical signals over optical fibers. Optical communications modules include optical transmitter modules, optical receiver modules and optical transceiver modules. An optical transmitter module has optical transmit capability, but does not have optical receive capability. An optical receiver module has optical receive capability, but does not have optical transmit capability. An optical transceiver module has both optical transmit and optical receive capabilities.
In an optical transmitter or transceiver module, one or more light sources (e.g., laser diodes) generate amplitude modulated optical signals that represent data, which are directed by an optics system of the module into an end of one or more transmit optical fibers of an optical fiber cable. The signals are then carried over the transmit fiber to a receiver node of the network. In an optical receiver or transceiver module, an optics system of the module receives optical signals output from an end of one or more receive optical fibers of an optical fiber cable and directs the optical signals onto an optical detector (e.g., a photodiode), which converts the optical signals into electrical signals. The electrical signals are then processed to recover the data bits contained in the signals.
The optical fiber cables have connectors on their ends (e.g., LC connectors, MTP connectors, etc.) that are adapted to mate with receptacles disposed in a housing of the optical communications module. One type of known connector that is used for this purpose includes a mechanical transfer (MT) ferrule that holds the end portions of a plurality of optical fibers in respective tube-like structures formed in the ferrule. The tube-like structures of the MT ferrule extend to respective openings formed in an outer end face of the ferrule. The end faces of the fibers are polished and are flush with the outer end face of the ferrule to provide a one- or two-dimensional array of fiber end faces disposed in the outer end face of the ferrule.
The MT ferrule has two precisely molded alignment holes formed on either side of the array of openings. The two alignment holes are shaped and sized to receive two steel guide pins disposed on an outer end face of a mating MT ferrule that is disposed within the receptacle of the optical communications module housing. The mating MT ferrule has an array of lenses disposed in the outer end face thereof that are in precise alignment with the array of fiber end faces disposed in the outer end face of the MT ferrule of the connector when the two ferrules are engaged with one another in a mated configuration. When the ferrules are engaged with one another in the mated configuration, features of the module housing and of the connector hold the ferrules rigidly to prevent movement of the ferrules relative to one another. This rigid mated configuration is intended to ensure that the array of fiber end faces of the connector MT ferrule and the array of lenses of the module MT ferrule are maintained in precise alignment with one another.
Although the features of the module housing and of the connector generally prevent movement of the ferrules relative to one another, a very small amount of relative movement can occur when forces are exerted on the connector, i.e., when the connector is wiggled. Such relative movement can result in the occurrence of optical losses, typically referred to as wiggle losses. Wiggle losses result in signal degradation that can detrimentally impact performance. If MT ferrules are multimode ferrules, the wiggle losses are generally considered negligible and are not viewed as detrimentally impacting performance. If the MT ferrules are single mode ferrules, however, wiggle losses generally cannot be ignored and can have a major detrimental impact on performance. For this reason, efforts have been made to incorporate features into the connector and/or into the module housing to prevent relative movement from occurring between the MT ferrules. Such efforts, however, have had only limited success.
Accordingly, a need exists for a way to prevent, or at least reduce, relative movement between the connector ferrule and the module ferrule when they are in the mated configuration to prevent, or at least reduce, wiggle losses.